So I understand through reading and asking questions that the Arduino Uno digital output pin should not acceed 40 mA output but the 5v pin can. This obviously is useful for powering relays with transistors I have found. So why is it that that the digital output pin can't source more than 40 mA but the 5v can? And what is the limit on what the 5v pin can source and why would that not be listed on the Arduino Uno SMD? Just a couple questions from someone new to this. Thanks guys!